1. Field of the Invention
The present invention relates to a method of and an apparatus for shaping a waveform of an input signal and to a method of and an apparatus for generating a threshold for a waveform shaping.
2. Description of Related Art
In a case where a logical processing is achieved on an input signal, when a decoding of the input signal is conducted to attain a logical value (1 or 0) represented by the input signal, it is a common practice that the input signal is processed through a level discrimination based on a predetermined threshold value to be converted into a logical signal expressing a logical value 1 or 0 depending on the discrimination level thereof. However, when the input signal contains a relatively large component of noise, there may be developed a wrong logical value. In order to remove noises, a high-pass filter (HPF) and/or a low-pass filter (LPF) have/has been employed in the prior art; however, necessary signal components other than the noises may be disadvantageously removed by the filter(s) in some cases.
The noise reduction has been an essential problem, particularly, in the fields of data communications. For example, in order to improve the signal-to-noise (S/N) ratio of a signal transmitted through a modulation system such as an amplitude shift keyinq (ASK), a frequency shift keying (FSK), or a phase shift keying system, there have been utilized an analog filtering, a digital filtering, etc. However, noises contained in signals supplied via a transmission route of a considerably low quality cannot be easily removed therefrom, which inevitably increases the size of a circuit or a software system for the noise filtering operation.